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In chemistry, bond order is a formal measure of the multiplicity of a covalent bond between two atoms. As introduced by Gerhard Herzberg, [1] building off of work by R. S. Mulliken and Friedrich Hund, bond order is defined as the difference between the numbers of electron pairs in bonding and antibonding molecular orbitals.
In a molecule such as H 2, the two electrons normally occupy the lower-energy bonding orbital, so that the molecule is more stable than the separate H atoms. He 2 electron configuration. The four electrons occupy one bonding orbital at lower energy, and one antibonding orbital at higher energy than the atomic orbitals.
Antibonding interactions between atomic orbitals are destructive (out-of-phase) interactions, with a nodal plane where the wavefunction of the antibonding orbital is zero between the two interacting atoms; Antibonding MOs are higher in energy than the atomic orbitals that combine to produce them. Nonbonding MOs: Nonbonding MOs are the result of ...
The energy level of a non-bonding orbital is typically in between the lower energy of a valence shell bonding orbital and the higher energy of a corresponding antibonding orbital. As such, a non-bonding orbital with electrons would commonly be a HOMO (highest occupied molecular orbital).
The difference in energy between the ionized and ground state gives the two ionization energies. As in benzene, in substances such as beta carotene , chlorophyll , or heme , some electrons in the π orbitals are spread out in molecular orbitals over long distances in a molecule, resulting in light absorption in lower energies (the visible ...
However it remains useful and customary to differentiate between different types of bond, which result in different properties of condensed matter. In the simplest view of a covalent bond, one or more electrons (often a pair of electrons) are drawn into the space between the two atomic nuclei. Energy is released by bond formation. [8]
A stereoelectronic effect generally involves a stabilizing donor-acceptor (i.e., filled bonding-empty antibonding, 2-electron 2-orbital) interaction. The donor is usually a higher bonding or nonbonding orbital and the acceptor is often a low-lying antibonding orbital as shown in the scheme below.
Sigma bonds occur when the orbitals of two shared electrons overlap head-to-head, with the electron density most concentrated between nuclei. Pi bonds occur when two orbitals overlap when they are parallel. [9] For example, a bond between two s-orbital electrons is a sigma bond, because two spheres are always coaxial. In terms of bond order ...